Process for the production of toluol



Jan. 8, 1946. F. 'M MCMILLAN ETAL 392,398

PROQESS FOR THE PRODUCTION OF TOLUOL Filed July 25, 1940 2 svhets-,sheet1 Invzniors: Frank M. McMillan George. Edward Lzdhokn Bg their Aornzq:

Jan. 8, 1946. F. M. MCMILLAN ETAI. 2,392,398-

PRocEss FOR THE PROISUGTION oEToLUoL Szparjaor,

Figli Inventors: Frank M. McMillan Gzorqz Edward Lzdholm crackeddistillates.

Patented Jan. 8, 1946 P-ROCESS FOR THE PRODUCTION F TOLUOL Frank M.McMillan, Berkeley, and George' Edward Liedholm, Long Beach, Calif.,assignors to Shell Development Company, San Francisco, Calif., acorporation of Delaware.

Application July 23, 1940, Serial No. 346,972

Claims.

The present invention relates to a process for the production of toluolfrom naphthenic distillates. An object of the invention is to provide a'method whereby commercial grades of toluol Y suitable for nitration,solvent use, and the like may be produced in a most economical mannerfrom available naphthenic hydrocarbon fractions of natural and/orsynthetic origin.

Toluol is one of the primary compounds upon which aromatic chemistry isbased. It is employed in large quantities as a starting material for thesyntheses of a great variety of useful products such as dyestuls.Explosives, drugs, flavors, perfumes, photographic developers, plastics.intermediate chemicals, and many others.

Virtually the only source of toluol is, however, a

by-product from the distillation of coal, being recovered in a yield ofabout 0.00125% based on the goal treated or about 0.25% based on thecoal-tar obtained. Consequently, the supply of toluol is primarilydependent upon the condition of the steel and coal-tar industries and isin any case limited. Aside from the numerous uses where its applicationis more or rless obligatory, toluolhas a great many potential uses whichhave' been curtailed by its limited supply and relatively high'price. Asa consequence considerable attention hasbeen given tothe possibility ofproducing toluol from other sources.y

This problemhas been considered from two angles. The rst of these is torecover toluol from aromatic petroleum fractions, particularly It isknown that distillates from certain petroleums and most highlycracked-distillates contain appreciable quantities of aromatic hydrocarbonsfrom which it is possible to recover highly aromatic distillates andeven relatively pure aromatic hydrocarbons by a suitable combination ofsteps involving fractionation and extraction. The recovery of toluolfrom such distillates is, however, quite diilicult and has not proven tobe economical. In the first place, only a small proportion of thearomatic hydrocarbons in these distillates is toluol, and consequently,large quantities of material must be processed to recover relativelysmall yields. Furthermore, the toluol in these distillates, even after apreliminary close fractionation, is present in an extremely complicatedmixture of hydrocarbons from which it is most difficult to separate atoluol of satisfactory purity. For some applications, such in particularas its use as a solvent, pure toluol is not necessary. For most of itsapplications, however, particularly where it is used as a startingmaterial in various chemical syntheses, toluol of at least 98% purity isdemanded. One of the major uses of toluol, for

example, is in the production of T. N. T. Toluol for this purpose mustbe water-white, have a boiling range of not more than 1 C., and have aspecific gravity at 15.5/15.5 C. between 0.866 and 0.874. It mustfurthermore pass the standard sulphuric-acid wash test which meansy thatit must be free of all but the minutest traces of oleilne hydrocarbonsand other impurities which are normally present inconsiderablevuquantities in the parent petroleum distillate. It is knownthat during the World War T. N. T. was produced from relatively impuretoluol fractions obtained from petroleum distillates. This, however. ne-

cessitated executing the nitration step-wise with intermediatetreatments for the removal of the impurities and was only resorted todue to the emergency at the time. While toluol of sufficient purity canbe separated from cracked distillates if the separation and purificationprocesses are carried far enough, the low yields obtained and theexpense of the recovery generally make such processes impractical forcommercial application.

The other approach to the problem is the synthesis of toluol fromnon-aromatic hydrocarbons.

It has long been known that hydroaromatic hydrocarbons may becatalytically dehydrogenated to laromatic hydrocarbons, Thus, it hasbeen shown in the laboratory that toluol may be easily produced frommethylcyclohexane by catalytic dehydrogenation. While this has long beenknown it has not led to the commercial production of toluol dueprimarily to the lack of a sultable source of methylcyclohexane. It isknown that certain naphthenic distillates contain appreciable quantitiesof methylcyclohexane; Here again, however, the small yields anddiillculty of separation of a commercial grade of toluol detract fromthe practicability of the process.

Quite recently it was discovered by Moldavskii and co-workersthat cyclichydrocarbons can be produced catalytically from open-chain hydrocarbonsby a new reaction' now known as cyclization. Thus, it-has been shown by4laboratory experiments that fair yields of to'luol may be produced fromnormal heptane, Z-methylhexane, 3-

methylhexa-ne and the corresponding oleilnes. y

The preparation of toluol from these open-chain hydrocarbons may beeffected .catalytically by passing vapors of the hydrocarbon over acyclization catalyst u nder appropriate conditions whereby asimultaneous dehydrogenation and by cyclization-dehydrogenation.

According to the process of the invention, we produce toluol fromnaphthenic distillates. By naphthenic distillates we mean hydrocarbondistillstes of natural or synthetic origin, containing 2 h i ceases anappreciable quantity of'naphthenic and parafnnic hydrocarbonshavingseven carbon atoms in the molecule. Suitable naphthenic distillates areobtained from a large number of crude petroleums. A few typicalcrueles'k from which suitable naphthenic distillates may be obtainedare. for

' example, Los Angeles Basin crude, Huntington Beach crude, DominguezHill crude, Ventura crude and El Capitan crude. The naphthenlcdistillate is preferably fractionated to separate a 10 Normal'heptane209.2" I".

2-methylhexane 194 F. 3-methylhexane 197.3 F. 20

This fraction, if from a naphthenic distillate, also Vcontainssubstantially all of the methylcyclohex- A,boilina' below the initialboiling .pOint of the desired fraction is removed overhead. The bottomsfrom this still pass to a second still wherein the 35- desired fractionis taken off overhead. The quantity of this fraction will vary accordingto the character of lthe distillate, but in most cases will be a sizablefraction. Typical analyses of these fractions from such `crudes are, forexample: o

Aromatic hydrocarbons 1-10 by weight Naphthenic hydrocarbons 15-75 byweight Parailln hydrocarbons; 25-85'by weight It is notpractical,-however, toproduce toluol 45 directly from such naphthenicfractions.

This is due primarily to the fact that .when subjecting such commercialfractions to a catalytic dehydrogenation-cyclization treatment theactive. life of `thec'atalyst is very short. This requires frequent 50stopping of the reaction and reactivation of the catalyst. Thereactivation treatment, which is eected by carefully burning depositedcarbonaceous material from the catalyst under 'controlled conditions,greatly decreases the economy of the c5 process since it istime-consuming, causes loss v of material. causes a gradual permanentloss of the catalyst activity. and requires the handling of large.quantities of reactivating and ushing gases. The results obtained uponsubjecting such @0 moved, the active life of thedehydrogenationfractions to a conventional dehydrogenation treatment areillustrated bythe following examf Die:

Example t A straight run naphthenic gasoline was fractionated to prepare9.190-230" F. vheart cut. A detailed investigation of its compositionshowed that it contained C1 components inthe following volume ratlos: l

points of these convertible paraiiin hydrocarbons .l5 are:

This material was mblected to a catalytic dehydrogenatlon-cyclizationtreatment under the following conditions:

Catalyst=Chromium oxide supported upon activated alumina (11% Cr.)Temperature=975 F.

Time=6 hours v Space velocity=0.73 vol. liquid/vol. catalyst/hourPressure: 15 lbs/sq. in. exit pressure Pure n-heptane, or puremethylcyclohexane, or a Asynthetic mixture of pure n-heptane and puremethylcyclohexane, when treated under these conditions, give excellentyields of toluol with little formation of carbon and gas. The abovefraction, howeverI afforded a conversion to toluolof only about 7% to10% (i. e. 15% to 17% .toluol in the product). Moreover, thecarbonaceous material deposited on the catalyst amounted to 4.6% byweight of the feed treated, and approximately 13% by weight of the feedWas`converted to gases. Under optimum conditions it required about 4hours to regenerate the catalyst.

According to the process of the present'invention, not only are theyields of toluol obtained from any given naphthenic distillate muchgreater, but the decline in the catalytic activity of the catalyst ismuch slower and less time is required for regeneration, and a crudetoluol is produced from which commercial grades of toluol may berecoveredv more economically.

It is found that the above-described fractions from naphthenicdistillates invariably contain considerable quantities of alkylatedcyclopentanes, such in particular as:

Bening point. r.

1.1-dimethy1cyclopentane 189.5 1,3-dimethylcyclopentane 195.31,2-trans-dimethylcyclopentane 197.2 1,2-cis-dimethylcyclopentane 210.6

Other hydrocarbons which are usually found to be present to variousextents include:

3,3-,dimethylpentane 186.8 2,3-dimethylpentane 193.5 '3-ethy1pentane199.9

Propylcyclobutane 210.2-212 2,2,4-trimethylpentane 210.7

These latter hydrocarbons when present act pri marily as inert diluentsand are only detrimental insofar as they make the recovery of the toluolmore dimcult. 'I'he above-mentioned alkyl-cyclopentanes, on the otherhand, are found to be very' detrimental,y small quantitiesin thehydrocarbon fraction to be treated, they cause a rapid deterioration ofthe activity of the catalyst. It is vfound that if these detrimentalalkyl-cyclopentanes are recycllzation catalyst is greatly improved, muchless frequent reactivation of the catalyst is required,

and the process is made much more economical. According to the processof the present invention, these detrimental-acting dimethylcyclopentanesare not only removed from the hydrocarbon fractions to be treated, butthey are converted into toluol. thus materially increasing the .70yield. Tne removal of these poisoning dimethylcyclopentanes isy effectedby subjecting them to asuitable isomerization treatment whereby they"are converted to a large extentto methylcyclo- Il auch a hydrocarbonfraction from a naph- When present, even in quite theme dmuate, boiling:of example between' lao' and 230 F., is subjected Ato an appropriateisomerization treatment. it is found that a material improvement yin theAyield of toluol and economy of the process results. j We found, how-vever, that a much greater improvement isobtained if the naphthenicdistillate is first separated into two fractions, one containing themajor part of the normal heptane and methylcyclohexane (for instance,boiling above 200v F.) and the other containing the larger part of thedimethylcyclopentanes and methyl hexanes (for instance, boiling below200 FJ, and only the latter is subjected to the isomerization treatment.This improved method .for producing toluol from such naphthenicdistillates is more fully described and claimed iny our copendingapplication SerialNo. 339,732, vfiled June l0, 1940.

We have now found that the method of oui- According to the process-ofthe present ininto a lower-boiling fraction (boiling, for example, up toabout 218 F.) containing the maior portion of the dimethylcyclopentanesand the me'thylcyclohexane and a higher-boiling fraction (boiling, forexample, above about 218 F.) containing the major'portion of any toluolpresent along with various higher-boiling impurities. These fractionsare then treated as shown in the flow diagram, Figure I. Referring toFigure I,

it is seen that the lower-boiling of the two abovedescribed fractionstaken overhead in the third fractionating column is subjected to anisomerization treatment. The isomerate passes to a fractionating columnwherein itis separated into two fractions boiling below and above about210 F. The lower-boiling fraction from the isom- 1 erate which -containsconsiderable unconverted dimethylcyclopentane is subjected to a secondisomerization treatment in a second isomerization unit and then toanother fractionation. 'I'he lower-boiling fraction from the isomeratefrom the second isomerization unit contains any unv converteddimethylcyclopentanes `and is removed from the system. Thehigher-boiling fractions from the fractionation of the isomerates aresubjected to, a catalytic aromatization treatment. 'I'he product fromthe aromatization treatment is fractionated to remove ,higher-boilingmaterials and the overhead fraction, together with the toluol fractionfrom the original naphthenic distillate, is passed to a recovery unitwherein toluol of the desired purity is recovered.

In the above description of the process the various fractions have beendesignated and-described by their primary constituents.- The preferredboiling rangesof the various fractions are shown in Figure I. It will beapparent, however.

that certain deviations from the preferred boiling ranges shown arepossiblev without departing from the spirit of the invention. Thus, forexample, the fractionation in the third fractionating unit is designedto separate the distillate into a lower-boiling fraction containing thedimethyl-v ture. such, for instance, as about 200 to'400 0-1cyclopentanes andl methylcyclohexane and a higher-boiling fractioncontaining as much' of any toluol present as may be convenientlyseparated without excessive loss of valuable methylcyclohexane from thelower-boiling fraction.

.When using conventional fractionating equipment .the separation betweenthese twofractions is preferably made at about 218 F. Av certain amountof deviation is, however, permissible and may even be advisable incertain cases. The initial boiling point of the lower-boiling fractionmay vary considerably, for example, from about F. up to about 195 F. Ifthe initiaiboiling point is chosen much below 190 F. more nonconvertiblehydrocarbons are included. On the other hand, if the initial boilingpoint is chosen much above 190 F. a loss in toluol yield may result. Ingeneral, the initial boiling point of the lower-boiling fraction ischosen at about 190 F.,

for example, 180 F. to 195 l1".` 'I'he final boiling point of thehigher-boiling or toluol fraction is preferably chosen somewhatabovef220 F., for example, 225 F. to 240 F. Although higherboilingmaterial may be included in the fraction.

its presence is in general undesirable since it makes the recovery ofpure toluol more dlmcult.

According to the present process, the lowerboiling of these twofractionsis subjected to an i isomerization treatment. This may beeffectedV by contacting the' fraction in they liquidl or vapor phase,preferably in the liquid phase, under suitable conditions with anisomerization catalyst, a hydrogen halide promoter, and, if desired,hydrogen. .Preferable isomerization catalysts are those comprisinganhydrous aluminum chloride and/or aluminum bromide. Of these, aluminumchloride is preferred since it is less expensive, easier to employ andhas much less tendency than aluminum bromide to cause degradation of thenaphthenic hydrocarbons. Other acid-acting catalysts of theFriedel-Crafts type such as the halides of Zr,l Zn, Sn, Be, Nb, Ta, Sb,B, Cu and Cd may also be employed if desired in conjunction with thealuminum chloride. T he catalyst may, if desired, be employed as vasolid, either in suspension in the liquid reaction mixture or as a fixedbed. In the latter case it is preferably employed as lumps, granules orpellets of suitable size, preferably deposited upon or mixed with asuitable solid support. Particularly effective catalysts are producedwhen aluminum chloride is supported upon or `inti4 mately mixed with oneof the various preferably adsorptive siliceous and/or aluminousmaterials of natural or synthetic origin which contain an .appreciableamount of firmly-bound water. Suitable materials of this category are,for ex-Av ample, the naturally-occurring minerals and clays such as pipeclay, bauxite, fullers earth, bentonite, Florida earth, meerschaum,kaoline, infusorial earth, kieselguhr, diatomaceous earth and the like:the various treated clays and claylike materials such as TonsiL Cel,lte,Sil-O- Cel," Terrana and the like; and artificially prepared materialssuch as Activated-Alumina, silicaI gel, the artificial permutites andthe like` These materials are preferably heated in a dry atmosphere at amoderately elevated temperauntil they substantially cease to give oilwater.

^ -Although these materials produce preferred catalysts when combinedwith aluminum chloride. othersupporting materials such as activatedcarbon, coke, crushed brick, pumice and ("the like While solid catalystsmay be suitably employed, we have developed an improved and advantageousmethod whereby the isomerization treatment may be eected in a continuousmanner using liquid catalysts. Particularly suitable liquid catalystsare those-of the Gustavson (C. 1903 II,

1113) and Ansolvo (German Patent No. 535,473)

acid types wherein aluminum chloride is in combination with variousorganic compounds such as organic acids, ethers, esters, hydrocarbons,etc. and those of the metal double-salt type -in which the aluminumchloride is in loose combinationV with similar metal halides such, forinstance, as the halides of Sb, Sn, Zr, Cu, Ti, Na, K, Li and the like.By employing aluminum chloride in combination with certain of thesemetal halides, ex-

,cellent isomerization catalysts may be prepared which melt tofree-owing liquids at very moderate temperatures and may be pumpedthrough the reaction system with or counter-current'to the organicmaterial to be reacted therewith to form the complex catalyst isintroduced via line I1. This may be any one or a mixture of a greatnumber oi' organic compounds. In case the complex catalyst is one of theGustavson type (C. 1903 II, 1113) the liquid added may bean aromatic-hydrocarbon or a hydrocarbon mixture rich in aromatichydrocarbons.Aromatic hydrocarthe hydrocarbon fraction'to be isomerized. The

detrimental when employing iixed beds of cat` alysts. When employingfluid catalysts, hydrocarbon fractions containing small amounts ofoleilnes and/or aromatic hydrocarbons may be treated without difnculty.These liquid catalysts,

moreover, have a considerably milder action and in general are much lessprone to cause degradation of the naphthenic hydrocarbons. Also, theyallow theV isomerization to be eiected in simple' apparatus in acontinuous and most practical manner. A flow diagram of a suitableisomerization unit employing this principle is illustrated in 'theattached Figure II. Referring to Figure II,

the hydrocarbon to be'treated is fed from a storv age tank l via pump 2to a circulating pump 2 wherein it is mixed with a liquid catalyst andpromoter and circulated through a heater 4 and time tank 5, and back tothe circulating pump 3 via a valved line 6. The time tank 5 ispreferably. equipped with perforated baiiies or other means to insurethorough contact with the hydrocarbon and liquid catalyst. All or aportion of the material passing through time tank 5 is withdrawn to aseparating device 1 wherein the liquid catalyst is separated from'thebulk .of the hydrocarbon. The liquid catalyst from' separator 1 isrecycled tothe circulating pump 3 via valve 8 and line 0'.

A portion of the partially-spent liquid catalystmay be continuously orintermittently removed i! desired via valved outlet 9 and an equivalentamount of fresh catalyst may be added via pipe Il. The hydrocarbon fromseparator i is passedv through a cooler Il and lter I2 to remove anyglobules of suspended catalysts and is then passed to tank I3.

The assembly of apparatusillustrated diagrammatically in Figure II- isadapted for the use -of liquid. catalysts of the above-mentionedGustavson or Ansoivo acid types. 'I'he catalystmay be prepared in anykconventional manner and supplied to the system. ior instance.' via linei0. For the sake of completeness provision is also made bons. aS aclass, are generally suitable. Thus, for

example, benzol and the various' alkyl derivatives thereof may be used.Particularly suitable catalysts of this type may be prepared froml thesocalled bright-stocks or Edeleanu Aextracts obtained by the extractionof aromatic-containing distillateswith sulphur dioxide. These catalystsare found to contain approximately twice as much aluminum chloride, forexample, as cata' lysts of the same general type prepared from benzol ortoluol. They therefore have a much longer life. Catalysts of this typeare described in United states Patents Nos. 1,671,517, 1,586,357,1,999,345 and British Patent No. 7,112-(1914). Aromatic extractsobtained by extraction with other selective solvents may, of course,likewise be employed.

The isomerization treatment is preferably executed in the presence of ahydrogen halide promoter such, for example, as hydrogen chloride. 'I'heamount of promoter preferably `employed depends upon the activity of thecatalyst and the prevailingtemperature, and may vary from asmali amountsuch as about 0.05% up to several percent. In one preferred" method ofoperation, wherein the hydrocarbon fraction is treated in a continuousmanner in the liquid phase, a consid erable excess of hydrogen chloride(forexample,

a partial pressure of hydrogen chloride vapor of umn i9 wherein the HCIpromoter and any other lower-boiling material is` taken, ofi' overhead.The overhead fraction ispassed through a cooler 20 into a vessel 2l.Condensed liquid in vessel 2i is pumped back to the stripping tower toserve as reiiux. The bottom product from tower i9 is passed through acaustic scrubber 22 to remove any last traces of promoter and is thenstored in tank 23. The hydrogen chloride promoter separated from theproduct in the stripping column is recycled back to the isomerizationsystem via line 2l. The hydrogen halide (and hydrogen, if this is used)recycled to the system is preferably passed through a drier 26containing a mutable drying agent such as' CaClz, P205, activatedalumina, or the like. Small amounts of excess gas may be vented fromtime to time by valved outlet 21. Make-up hydrogen chloride is suppliedto the system from any convenient source suchas a high-pressure cylinder24. As pointed out above,

however, when using liquid catalysts the isomerifor the preparation ofthe catalyst in the now diagram 'of Figure II. This apparatus, whichmayl be considerably modined if desired. comprisesl a mixingcvessel ilinterconnected in a circulatory system via circulating pump l5 to asmall chainber Il. Aluminum chloride or other catalyst is 7o halide perse, the hydrogen chloride or other hyzation process may be executed withonly very smallv amounts of hydrogen chloride promoter, for instance,less than 1%. In such cases, it may be more economical not to attempt torecover andrecycle the promoter. In this case the product from tank lmaybe simply caustic-washed and sent to storage. Instead oi feeding inhydrogen drogen halidel promoter may be carried to the reaction zone,dissolved in one oi the reactants, or may be generated in the reactionzone from added materials which under the reaction conditions cbargedtothe mixing vessel Il and a quantity o! '7l react or decompose toliberate hydrogen halide.

a,saa,sos

suitable materials which may be added for una purpose are, for example,organic halides such as organic alkyl halides, organic hydroxycornpounds such as the various phenols and alcohols,

inorganic salts containing molecularly-bound hy.. drogen halide such asPbSOi-ZHCI, CuSOrZHCl and the like.

The isomerization maybe effected over a wide range of temperaturesdepending upon the space velocity, concentration of promoter employedand upon the activity of thecatalyst. Althoughetemperatures ranging fromabout room temperature v up to about 400 F. may be employed, the isomerlMost naphthenic ization may be eilected economically at quite 'motel'.or if desiredfby effecting theisomeization treatment in the presence loihydrogen. Hydrogen, if employed, may be conveniently recycled with thehydrogen halide promoter. Although -the use of hydrogen is not generallynecessary-.-

provision for its use is shown in Figure II. Thus, if hydrogen isrecycled along with thepromoter, make-up hydrogen may be added'fromcylinder 25.

The isomerate from the first ixonierization treatment is, according tothe present process,

subjected to a suitable fractionation designed to separatemethylcyclohexane Aoriginally present and formed in the isomerizationfrom unisomerized dimethylcyclopentanes and other lower-boilingnon-aromatizable constituents. As shown in Figure I, the fractions may,for example, be cut at abouty 210 F. The lower-boilingdimethylcyclopentane fraction from the isomerate is subjected to asecond isomerization treatment, as described, and refractionated. Inthis way a maximum yield of aromatizable hydrocarbons is separated witha minimum of detrimental dimethylcyclopentanes.

The higher-boiling fractions from the' isomerates (boiling, for example,between `about 210 and 215 F.) are subjected to a catalyticaromatization treatment in the usual manner. 4This may be mostpractically effected in one apparatus employing the recombinedfractions, but it may consists almost entirely of toluol and ispreieralso be effected separately with each fraction lfff for anyreason, this is desired. The dehydrogenation treatment may'be eiected byany ot the conventional methods, using any of the convene tionaldehydrogenation and/or cyclization cata lysts. In general, however, thedehydrogenationcyclization treatment is effected by passing they v thereaction is preferably executed under a considerable hydrogen pressure,for example, from 20 to atmospheres. In other cases, for example, whenemploying a catalyst comprising an oxide of a metal of the 4th, 5th or6th group of the pending upon the temperature activity ot the catalyst,space velocity, etc. Likewise, the temperature may vary considerably.Temperatures in the order of 900 to 1100 F. are, however, generally mostsuitable.

While the above-described process illustrated in Figure I of thedrawings is entirely practical and suitable for general application withmost naphthenic distillates. in certaincases it may be desirable tomodify thetreatment somewhat. distillates contain small amounts oftoluol. This toluol. although usually Vtoo small in amount to be ofpractical value per se, is recovered in the above-described process andincreases the toluol yield. In certain cases,

however, it may be found that the amount of toluol naturally present inthe naphthenic distillate is too small to warrant its recovery. In suchcases the third fractionating column may be eliminated and theoverheadfraction from the second fractionating column, which is thenpreterably cut at about 190 to 218 F., may be passed directly to the rstisomerization unit. Also, it may be advantageous to subject theisomerate to a second fractionation to removesmail amounts of higherboiling products which may be formed under certain conditions prior tosubjecting itv to the catalytic aromatization treatment. A. fractionatmgapparatus for this purpose is shown in Figure I in broken lines. Also,the fractionating column between the aromatization unit and the recoveryunit (Fractionating unit VI in Figure I) may be eliminated, if desired.by returning the product from the aromatization unit directly to thenaphthenic feedifor instance, to the feed to 4 Fractionatmg units I orII).` In general, however, the'product from the aromatization unit ablyfractionated in' a separate unit (Plractionating unit VI). 1 y

The process of the present invention provides a ymeans whereby toluol ofalmost any desired degree of purity may be obtained in high andpractical yields from naphthenic distillates. Due to the substantiallycomplete `removal of detrimental dimethylcyclopentanes from the feed ,tobe aromatized, the catalytic aromatization in the present process ismuch more efficient. The aromatization in the presentjprocess may, ingeneral, be effected with exceptionally long and high ilonversions.,Also. the feed to the aromatization step, which is the most costlyphase, is reducedvto a minimum without impairing the toluol yield. Theproducts obtained from the dehydrogenation-cyclization treatment,according to the present process, are generally much higher in toluoland much lower in undesirable hydrocarbon impurities than those obtainedfrom other methods. In many cases it is ofsulcient purity to be usedwithout further purification as a solvent and the like where a toluol othigh purity is not required.

l A'n advantage of the present process is that the toluol may berecovered from the product in almost any desired degree of purity byrelatively simple methods and with greater eillciency and economy. Thisis due largely to the fact that a purities have been converted intotoluol. Thus.

Y it is generally possible to produce almost a complete yield of toluolvmeeting the stringent requirexnents for nitration by a simpleextractive periodic system, the process is preferably executed underabout atmospheric pressure. for example, from 1 to 4 atmospheres, with amol ratio distillation. In some cases awash with dilute sulphuric acidmay be required.

The recovery of toluolof the desired purity '0f hydmen raninl from 0 upto about 8, de- 15 may be eirected by any one orcombination orconventional methods such as fractional distillation, azeotropicdistillation, solvent extraction, extractiva distillation,crystallization, or thelike. E'xtractive distillation. being both highlyeffective and economical. is a preferred method. A suitable recoveryunit employing extractiva distillation is illustrated in the iiowdiagram offFigure Ill'. Referring to Figure III, the toluolcontainingmaterial from the dehydrogenationunit is fed to a fractionating columnI, provided with condenser 52, collector 53, and means 54 Ifor returninga part of the overhead material to es-` tablish reflux. Fractionatingcolumn Bl is adjusted to' remove the greater part of the nonconvertedand lighter-boiling hydrocarbons. This lighter overhead fraction may bedisposed of for other purposes such as motor fuel or may, depending uponits composition, be recycled. If it consists largely of open-chainparaiiins` including normal heptane. it may be recycled through thedehydrogenation-cyclization unit.

. creased yields of substantially pure toluol while If, as is sometimesthe case, it also contains any appreciable quantities of alkylcyclopentanes, it

is preferably recycled through the isomerization treatment. The bottomproduct from fraction-4 ating column 5I may be subjected directly to theextractiva distillation treatment. However, Ait is often advisable tofirst remove a relatively pure toluolV fraction in a secondfractionating column 55. The bottom product from column 55 consists ofsmall amounts of higher-boiling impurities. This is withdrawn via line6B. The toluol fraction from column 55, after passing through the cooler51 and collector 58, is pumped via pump Stand line 60 to a column 6iadapted for extractive distillation. A suitable polar agent is fed at asuitable point near the top of the column in regulated quantity via pipe82 and automatic control means 63. The polar agent employed in theextractive distillation may be any 40 one of the many polar solventshaving a preferential solubility for toluol and preferably having ,atingor stripping column 65 wherein the toluol is separated from the polaragent. Substantially pure toluol ls removed overhead via cooler 66, colJlector 81, and is led to storage or to a dilute acid realizing maximumcatalytic efliciency which comprises separating from a naphthenicstraight run gasoline stock byfractional distillation a fraction boilingbetween about 190 F. and about 2l8 F., treating said fraction with analuminum chloride isomerization catalyst under isomerization conditions,separating the isomerizate by fractional distillation into a lowerboiling fraction boiling between about 190 F. and about 210 F. and ahigher boiling fraction, treating said lower boiling fraction of saidisomerizate with an aluminum chloride isomerization catalyst underisomerization conditions, separating the isomerizate by fractionaldistillation into a lower boiling fraction boiling between about 190 F.and about 210 F. and a higher boiling fraction, subjecting said higherboiling fractions from the isomerizates to catalytic dehydrogenationwith a dehydrogenation catalyst under dehydrogenation conditions, andrecovering substantially pure toluol from the dehydrogenated product.

2. In a process for the production o1' toluol` from naphthenic straightrun gasolines via cat. alytic dehydrogenation, the method of producingincreased yields of substantially pure toluol while realizing maximumcatalytic eiiiciency Awhich comprises separating from a napthenicstraightrun gasoline stock lby fractional distillation a fractionboiling between about 190 F. and about 218 F., treating said fractionwith an aluminum chloride isomerization catalyst under isomerizationconditions, separating the isomerizate by fractional distillation into alower boiling fraction boiling between about 190 F. and about 210 v F.and a higher boiling fraction, treating said .lower boiling fraction ofsaid isomerizate with/ an aluminum chloride isomerization catalyst underisomerization conditions, separating the isomerizate by fractionaldistillation into a lower boiling fraction boiling between about 190 F.and about 210 F. and a higher boiling fraction, separating the higherboiling fractions of said isomerizates by fractionalvdistillation into ahigher boiling fraction boiling above about 215 F. and a lower boilingfraction boiling between about 210 F.-and about 215 F., subjecting saidlastmentioned fraction to catalyticv dehydrogenation with adehydrogenationcatalyst under dehydrogenation conditions, and recoveringsubstantially pure toluol from the dehydrogenatedproduct.

3. In a process for the production of toluol from naphthenic straightrun gasolines via catalytic treatment Via pipe 58. The Dolar agent 1SIBCOV? 55V dehydrogenation, the method of producing inered as a bottomproduct via pipe 69. It may be' sent to storage and re-used in column6I.' Further details regarding extractiva distillation may be found inFrench Patent No. 815,302.

In the foregoing we have explained our mvention in considerable detailindicating various preferred embodiments as well as certainmodifications thereof. Numerous other suitable modifications, many ofwhich may afford slightlyfmore economical operation under certaincircumstances, will at once be apparent to those skilled in the art. Itis therefore to be lunderstood that the invention is not limited to theexact form or forms described and that all such modifications as fallwithin the spirit of the invention are intended to be embraced inthelanguage of the accompanying claims.

We claim as our invention:

1. In a process for the produ-'ation of toluol from creased yields ofsubstantially pure toluol' while .realizing maximum catalytic eiliclencywhich fractional distillation into a lower boiling fraction boilingbetween about 190 F. and about 210 F.

and a higher boiling fraction, treating said lower boiling fraction ofsaid isomerizate with'an aluminum chloride-isomerization catalyst underlsomerization conditions, separating'the isomerizate by fractionaldistillation into a lower boiling frac-` tion boiling between about 190F. and about 210 l F. and a higher boiling fraction,r subjecting saidhigher boiling fractions from the isomerizates to catalyticdehydrogenation with a dehydrogenanaphthenic straight run gasolines via.catalytic tion catalyst under dehydrogenation'conditions.

removing from the product oi' said dehydrogenation treatment byfractional distillation material boiling above about 230 F., andrecovering substantially pure toluol from the remainder.

4. In a process for the production of toluol from naphthenic straightrun gasolines via catalytic I dehydrogenation, the method of producingincreased yields of substantially pure toluol while realizing maximumcatalytic eiliciency which -an aluminum chloride isomerization catalystunder isomerizatlon conditions, separating the isomerizate by fractionaldistillation into a lower boiling fraction boiling between about 190 F.and about 210 F. and a higher boiling fraction, separating the higherboiling fractions of said isomer- Aizates by fractional distillationinto a higher boiling 'fraction boiling above about 215- F. and a lowerboiling fraction boiling between about 210 F. and about 215 F.,subjecting said last-mentioned fraction to catalytic dehydrogenationwith a dehydrogenation catalyst under .dehydrogenation conditions,removing from the product of 4said dehydrogenation treatment byfractional distillation material boiling above about 230 F., andrecovering substantially pure toluol from the remainder.

run gasoline stock by fractional distillation a fraction boiling betweenabout 190 F. and about y fraction with-an aluminum chlorideisomerization catalyst underlisomerization conditions, separating theisomerizate by fractional distillation into a lower boiling fractionboiling between about 190 F. and about 210 F. and a higher boilingfraction, treating said lower boilingv fraction of said isomerizate withan aluminum chloride isomerization catalyst underisomerlzation'condltions, separating the isomerizate by fractionaldistillation into a lower boiling fraction boiling between about 190 F.and about 210 F. and a higher boiling fraction, separating the higherboiling fractions of said isomerizates by fractional distillation into ahigher boiling fraction boiling above about 215 F. and a lower vboilingfraction boiling between about 210 F. and about 215 F.,'subjecting saidlast-mentioned fraction to catalytic dehydrogenation with adehydrogenation catalyst under dehydrogenation conditions, combining thedehydrogenated fraction with the above-said first higher boilingfraction boiling between about 218 F. and about 230 F., and extractingsubstantially pure toluol from said combined fractions.

v5. In a process for vthe production of toluol from naphthenic straightrun gasolines via catalytic dehydrogenation, vthe method of producing'increased yieldsof substantially pure toluol while realizing maximumcatalytic efiiciency which comprises separating from a naphthenicstraight run gasoline stock by fractional distillation a fractionboiling between about 190 F. and about 230 F., separating said fractionby fractional distillation into a lower boiling fraction boiling betweenabout 190 F. and about 218 F. and a' higher boiling fraction boilingbetween about 218 F. and about 230 F., treating said lowerboilingfraction with an aluminum chloride isomerization catalyst underisomerization conditions, separatlytic dehydrogenation with adehydrogenation.

catalyst under dehydrogenation conditions, combining the dehydrogenatedfraction with the above-said ilrst higher boiling fraction boilingbetween about 218 Frand about 230 F., and recovering substantially puretoluoll from said com-y bined fractions.

. 6. In a process forthe production of toluol from naphthenic straightrun Igasolinea via catalytic dehydrogenation, the method lof producingincreased yields of substantially pure toluol while realizing maximumcatalytic efilciency which comprises separating from a naphthenicstraight 7. In a process for the production of toluol from naphthenicstraight run gasolines via catalytic dehydrogenation, the method ofproducing increased yields of substantially pure'toluol while realizingmaximum catalytic eill'ciency which comprises separating from anaphthenic straight run gasoline stock by fractional distillation afraction boiling between about F. and about 230 F., separating saidfraction by fractional distillation into a lower boiling fractionboiling between about 190 F. and about 218 F, and a high- -er boilingfraction boiling between about 218 F.

and about 230 F., treating said lower boiling fraction with an aluminumchloride isomerization catalyst under isomerization conditions.separating the isomerizate by fractional distillation into a lowerboiling fraction boiling between about l190" F. and about 210 F, and ahigher boiling fraction, treating said lower boiling fraction of saidisomerizate with an aluminum chloride isomerization catalyst underisomerization conditions, separating the isomerizate by frac'. tionaldistillation vinto a lower boiling fraction boiling between about 190 F.and about 210 F. and a higher boiling fraction, subjecting said higherboiling fractions from the isomerizates to catalytic dehydrogenationwith a dehydrcgenation catalyst under ydehvdrogenation conditions,removing from the product of said dehydrogenation treatment byfractional distillation material boiling above about 230 F., andcombining the remaining fractions with the above-said first higherboiling fraction boiling between about 218 F. and about 230 F., andrecovering substantially pure toluol from said combined fractions.

8. In a process for the production of toluol from naphthenic straightrun gasolinas via catalytic dehydrogenation, the method of producingincreased yields of substantially pure toluol while realizing 'maximum'catalytic emciency which comprises separating from a naphthenic straightrun gasoline stock by fractional distillation a fraction boiling betweenabout 190 F. and about 230 1"., separating said fraction by fractionaldistlllation into a lower boiling fraction boiling between about 190 F.and about 218 l". and a higher boiling traction boiling between about218 F.,

and about 230 F., treating said lower boiling fraction with an aluminumchloride lsomerizaf tion catalyst under isomerization conditions.separatin'g the isomerizate by fractional distillation into a lowerboiling fraction boiling between about 190 F. and about 210 F. and ahigher boiling fraction, treating said lower boiling irac-y tion of saidisomerizate with an aluminum chloride isomerization catalyst underisomerization conditions, separating the isomerizate by iractionaldistillation into a lower boiling fraction .boiling between about 190 F.and about 210 F.

and a higher boiling fraction, separating the higher boiling fractionsot said isomerizates by fractional distillation into a higher boilingfraction boiling above about 215 F. and a lower about 215 11".,subjecting said last-mentio boiling fraction boiling between about 210E'. and 90 asnasoe y above-saidv iirst higher vboiling fraction boilingbetween about 218 F. and about 230 F., and extraeting substantially puretoluol from said combined fractions.

9. The method of claim 1 further characterized in that thedehydrogenation treatment'is eilected with a dehydrogenation catalystcomprising chromium oxide.

10. The method oi' claim 1 further characterized in that the recovery oftoluol from the dehydrogenated product is eilected by extractivedistillation. f

Y M. MoN. GEORGE EDWARDHOLM.

